Water can be “activated” by applying plasma in contact with the water, for instance by creating plasma inside (bubbles in) the water, or along a water surface. Plasma activated water (PAW) typically contains hydrogen peroxide, nitrates, nitrites, where peroxynitrite is formed due to a reaction with nitrite and hydrogen peroxide in an acidic environment, and is only present in PAW for period of approximately 15 minutes after activation. Further, PAW typically has a pH ranging from 0 to 7. The components of PAW and the low pH have proven synergistic antimicrobial effects against bacteria, biofilms, yeasts and other microorganisms. PAW can be used as a natural fertilizer, it enhances seed germination and stimulates plant growth.
Current PAW production methods employ either non-thermal (or cold) plasma or thermal plasma. Combining both has several advantages, but until now has never been realized. A non-thermal plasma essentially produces reactive oxygen and reactive nitrogen species (ROS, RNS) in the gas phase, which result in the formation of the products in the water.
In particular the production of ROS (i.e. hydrogen peroxide) is effective with non-thermal plasma. FIG. 1 shows a prior art graph of typical pH and concentrations for peroxide, nitrite and nitrate for both a thermal and a non-thermal plasma.
For the creation of RNS in the water, a thermal plasma is more efficient due to the relatively high temperature of such plasma, which yields higher concentrations with low creation of peroxide, where high temperatures decompose peroxide and peroxynitrite is an isomer of nitrate and very unstable, this component will always decompose quickly.
The production of nitrate as a result of the activation process has shown to be very energy efficient and can be used as an energy efficient alternative for the production of nitrogen components in fertilizers, currently produced by the high energy consuming Haber-Bosch process. The activation process has also shown to be efficient for the production of peroxide.
The wide range of potential applications requires a good control over the composition of the PAW. This is difficult with current methods, where higher product yields and higher production rates are required.
What is needed is a PAW production system and method that includes employing both thermal and non-thermal plasma, where the two plasma modes can be generated individually or simultaneously.